1. Field of the Invention
This invention relates to a light emitting device, more particularly to a light emitting device having at least two light emitting diodes (LEDs) and a photon-recycling member that converts a primary light emitted from one of the LEDs into a secondary light for emitting a multiple-chromatic light.
2. Description of the Related Art
U.S. Pat. No. 5,851,063 discloses a conventional lighting system that uses three LEDs, which emit lights in the wavelength ranges from 455 to 490 nm (blue light), 530 to 570 nm (green light), and 605 to 630 nm (red light), respectively, as a light source for emitting a trichromatic white light. The lighting system is disadvantageous in that the driving voltage of the red light LED is different from those of the blue light LED and the green light LED. As a consequence, two different circuits are required for the red and blue or green light LEDs, respectively, which complicates the lighting system and results in an increase in the manufacturing costs. In addition, when one of the three LEDs breaks down, particularly, when the red light LED breaks down, the lighting system can no longer emit white light.
Another conventional lighting system uses a blue light LED or a UV LED in combination with a fluorescent material for emitting white light. However, the luminous efficacy of the lighting system is greatly reduced by the fluorescent material. Moreover, the fluorescent material tends to deteriorate after a period of use.
Conventional photon recycling LEDs include an LED bonded to a wafer containing an active region which absorbs photons of a primary light emitted from the LED and remits a secondary light through photon recycling mechanism. However, the conventional photon recycling LEDs can only emit a complementary white light (a combination of blue light and yellow light) and cannot be fit well with the blue, green, and red color filters for serving as a light source in a backlight module of a liquid crystal display.